In the field of steerable radars and techniques, many of which are commonly used for surveillance of a given volume, it is frequently advantageous to enhance dwell times in each beam position in the searched volume. Enhanced dwell time should enable more effective discrimination against uninteresting reflectors such as rain, chaff or fixed background.
One of the previous techniques for enhancing dwell time is to employ a receive cluster of beams or beam components arrayed in elevation. The principal reason for the use of this technique as compared with other approaches such as the so-called pencil beam radar is that the use of such multiple beams provide longer dwell times in each beam position than the use of a pencil beam.
A fuller description of a system employing a cluster of beams or beam components arrayed in elevation is found in the article by Thomas E. Keast, "AN/TPS-70 Tactical Radar System" The Aviation Institute Journal, Winter 1987, pp. 25-27, and 42. See also Keast's article "Long-Range, Stacked-Beam Surveillance Radar" in DEFENSE SYSTEMS INTERNATIONAL, Sterling Publications, London 1988, at pages 222-224.
A variant of such systems is described in Radar Applications, edited by Merrill I. Skolnik, IEEE Press, New York, in the reprint starting at page 144: "Paper 3.2- A High Performance Tactical 3-D Radar for the 1980's" by K. F. Horenkamp et al. This article is also good source of definitions and explanations of terms and acronyms used in this area of the art.
There are, however, major disadvantages to the employment of a fixed cluster of beams arrayed in elevation. These disadvantages include at least the following four items:
(1) Fixed elevation coverage cannot be altered as a function of elevation angle to accommodate various blocking conditions near the horizon or the need to look below the horizontal level in cases where the radar installation is positioned on a hilltop.
(2) Heavy illumination of so-called ground clutter, which is the type of fixed background that usually occurs at or near the horizon, also is not avoided. This heavy illumination by the transmitted radiation, which must continuously illuminate the full elevation extent of the receive beam cluster, resulting in strong reflected returned radiation, occurs at all times requiring moving target indicator (Doppler) processing and sensitivity time-control processing to compensate to a much greater degree than if the heavy illumination of ground clutter could be reduced or avoided in the upper elevation beams.
(3) All beams or beam components arrayed in elevation must use the same pulse repetition frequency and pulse sequence even though the above-mentioned moving-target indicator processing needs may vary from beam component to beam component.
(4) Each pulse transmission can use only a single narrow-band waveform with a consequently limited set of electronic counter counter-measure capabilities (ECCM).
While a pencil beam radar can avoid the first three disadvantages, it operates at a severe disadvantage in providing the kind of dwell times which are highly desirable in this field of radar techniques.